The present invention relates to aircraft propulsion systems, and more particularly to a propeller and blade element for such a system.
Conventional propeller blade elements have the blunt leading edge configuration illustrated in cross-section as element 10 in FIG. 1. Under certain conditions, leading edge stagnated air develops at the blunt leading edge of the conventional blade and the blade can undergo a stall condition. FIG. 1 shows the air flow around a conventional airfoil in stall condition, illustrating the vortex formation at the leading edge, and the lack of laminar air flow.
Mark's Engineering Handbook, Section 11.4 ("Aeronautics" by J. J. Cornish, III) at page 11-69, shows the stagnation point, in FIG. 11.4.4, in respect to the leading edge of an airfoil.
Laminar air flow and vortex formation conditions have a bearing on the stall characteristics of airfoils such as propellers. Such characteristics have been the subject of considerable study and analysis. See, for example, "A Comparative Study of Some Dynamic Stall Models," T. S. R. Reddy, NASA Technical Memorandum 88917, March 1987, at pages 6-7.
It is therefore an object of the invention to provide a propeller blade element which substantially eliminates the formation of leading edge stagnated air.
A further object is to provide a propeller blade element which provides a laminar fluid flow.
Another object is to provide an anti-stalling and anti-noise propeller blade element having increased efficiency over conventional blade elements, and which is capable of operation under high aerodynamic loads and over a greater speed range without a variable pitch control than conventional propeller blade elements.